The present invention generally relates to the production of printed images on fabric substrates, and more particularly to a specially-treated ink transfer sheet which is used to thermally deliver ink materials to a fabric substrate in a manner which produces a vivid and stabilized (e.g. waterfast) printed image.
In recent years, the popularity of "personalized" printed clothing has greatly increased. For example, a variety of different techniques have been developed involving the production of custom-printed T-shirts and other clothing items. Of primary importance is the use of "transfer sheets" which contain monochrome (e.g. single color) or multi-colored printed images that are placed on a clothing item, followed by the application of heat thereto. As a result, the printed image on the sheet is "heat transferred" directly to the clothing item or other fabric substrate. This type of process along with representative ink transfer sheets and related procedures is discussed in a variety of references including U.S. Pat. Nos. 4,664,670; 4,758,952; 4,767,420; 4,980,224; 4,966,815; 5,139,917; and 5,236,801.
The basic ink transfer sheets of primary concern in the present case are commercially-available products which can be obtained from, for example, Foto-Wear, Inc. of Milford, Pa. (USA). These sheets normally involve three main layers, namely, (1) an inert backing layer which is ultimately removed and discarded; (2) a detachable release layer positioned on the backing layer which is designed for easy removal from the backing layer during the thermal transfer process; and (3) an ink receiving (e.g. ink absorbent) layer positioned on the release layer. In use, a printed image is initially applied to the ink receiving layer as discussed in greater detail below. Thereafter, the ink transfer sheet containing the printed image is positioned on a desired fabric substrate (e.g. a T-shirt or other clothing item) with the ink receiving layer (and printed image thereon) directly contacting the substrate. Heat is then applied by a conventional heated platen apparatus known in the art for thermal transfer purposes or a standard household iron in an amount sufficient to cause the release layer and accompanying ink receiving layer (containing the printed image) to adhere to the substrate. Because the release layer is typically produced from a low melting point polymeric composition, it softens substantially during the heating process which not only facilitates adhesion to the fabric substrate but also enables rapid detachment of the release layer from the backing layer. During or immediately after the application of heat to the ink transfer sheet on the fabric substrate, the backing layer is physically removed (e.g. peeled away) from the remaining layers of the transfer sheet. As a result, the release layer and attached ink receiving layer containing the printed image remain on the fabric substrate. In this manner, the printed image is effectively transferred to the substrate to generate a printed final product. It is important to note that the printed image (which is usually applied to the ink transfer sheet in a "reverse" configuration so that it will be properly oriented on the fabric substrate) is readily visible on the substrate since the release layer and ink receiving layer are substantially colorless (e.g. transparent). As a result, the printed image can be seen through these layers.
Heat-based ink transfer systems of the type described above have recently become available to consumers for in-home use. Consumers are now able to apply computer-generated or other images directly to a selected ink transfer sheet using commercially-available printing devices of conventional design. However, whether the printing process is being undertaken by consumers or on a large-scale commercial level, it is important that the printed image be stable or "waterfast" after it is applied to a selected fabric substrate. The term "waterfast" as used herein shall signify a printed image which does not smear, bleed, run, fade, or the like when exposed to moisture (e.g. water and/or water-based materials). If the printed image on the fabric substrate (e.g. T-shirt) is not sufficiently waterfast, it will progressively fade after repeated machine washings, thereby resulting in a product with a dull and indistinct character.
Prior to development of the present invention, a need existed for an effective thermal transfer process in which the resulting printed images remained clear, stable (e.g. waterfast), and fade-resistant over time. The present invention satisfies this goal through the use of a unique modified ink transfer sheet which includes chemical compositions that are capable of binding to charged coloring agents (e.g. dye molecules) in order to produce stabilized images. Likewise, the claimed invention is especially suitable for use in connection with thermal inkjet printing systems which enable the entire printing process to be accomplished by consumers at home. The claimed process and transfer sheets therefore represent an advance in the art of thermal transfer printing as discussed in greater detail below.